Currently marketed high-performance display devices, such as liquid crystal and plasma displays, typically employ two high-precision glass sheets, one as a substrate for the electronic circuit components and the other as a substrate for a color filter. The leading technology for making such high-quality glass substrates is the overflow fusion down-draw process, developed by Corning Incorporated, and described, e.g., in U.S. Pat. Nos. 3,338,696 and 3,682,609.
The fusion down-draw process typically utilizes a forming body comprising an upper trough portion comprising two upper trough walls and a trough bottom and a lower portion having a wedge-shaped cross-section with two major side surfaces sloping downwardly to join at a root. The upper trough walls and the major side surfaces of the lower portion form two continuous forming surfaces which join at the root. During operation, molten glass is filled in the upper trough and allowed to overflow the top surfaces (or weirs) of the trough, down along the two forming surfaces, ultimately converging at the root to form a unitary glass ribbon with two pristine external surfaces that have not been exposed to the surface of the forming body. The ribbon is drawn down and cooled to form an elastic glass sheet having a desired thickness and a pristine surface quality.
Consumer demand for high-performance displays with ever growing size and image quality requirements poses a challenge in terms of the manufacturing processes employed to produce large pristine glass sheets. The larger the glass substrate, the larger the forming body must be to manufacture the substrate. Traditionally, forming bodies are formed by cold isostatically pressing a single, unitary piece of refractory material, such as zircon. Understandably, larger isostatic presses are required to make larger forming bodies from a unitary refractory material. However, when taking into account the size reduction caused by the shrinkage of the green refractory during firing and the subsequent machining of the refractory substrate to produce the forming body, the size of the isopress required can become significantly greater as the desired size of the forming body increases. The high capital investment in such large isopresses may be cost-prohibitive, especially for larger glass substrates, such as Gen-10 (2850×3050 mm) and above.
Thus, there is a need in the industry for efficient and cost-effective processes for making larger refractory substrates from which larger forming bodies can be machined. U.S. Pat. No. 7,988,804 proposes methods for the manufacture of larger zircon blocks comprising bonding several smaller zircon components together using a bonding agent. However, while these methods have resulted in a marked improvement in the industry, such methods still have certain drawbacks, such as decreased strength, incompatibility, corrosion, and streaking issues. The methods disclosed herein may provide larger refractory substrates without the aforementioned drawbacks.